A fast purification method for recombinant human interferon-gamma, produced in E. coli, was elaborated. Human IFN-gamma accumulated in the cytoplasm of E. coli cells as inclusion bodies (IB). After lysis, the IB were isolated from the cell debris by means of a density gradient ultracentrifugation, and solubilized in 6 M guanidine hydrochloride. The subsequent refolding step was optimized for a maximal recovery of the biologically active dimer. Refolded IFN-gamma was then purified to homogeneity in a single cation exchange chromatographic step, yielding 12.5 mg protein per liter E. coil culture. The dimeric nature of the refolded protein was visualized by means of interchain cross-linking. In a subsequent Western blot the resulting derivative was recognized by a panel of five monoclonal antibodies, indicating that those epitopes on the protein surface remained unaffected upon cross-linking.